Inventories - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	Jul. 31, 2012	Jul. 31, 2011
Schedule of Inventory [Line Items]
Inventory	$ 219,863	$ 213,662
Subsidiaries valued inventory in first-in, first-out method	36,887	25,530
Inventory obsolescence reserve	$ 1,866	$ 2,039